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Archosauria includes Crocodilians, Pterosaurs, Dinosaurs (including Birds), and a variety of other extinct groups.

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Crocodylomorpha: Still extant - known from the Middle Triassic to present day. In brief: Low, flat skull. All but a few marine forms have 24 vertebrae cranial to the hip and 2 sacral vertebrae for attaching to the hip.

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Mesozoic marine reptiles are not dinosaurs. All are a variety of diapsid reptilies. We will survey them from approximately more primitive diapsid derivatives to somewhat more derived diapsid derivatives.

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Plesiosauria: Much larger than nothosaurs. Forelimbs and hindlimbs look much more similar. EXTREMELY elongate necks, even more so than nothosaurs. Note that despite paddle-like nature of hand (manus) and foot (pes), each still retains only five digits.

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Plesiosaurs have HYPERPHALANGY: additional segments to the digits of the fingers and toes.

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Cryptoclidus (plesiosaurid) Hydrothecrosaurus (elasmosaurid) Plesiosaurs have HYPERPHALANGY: additional segments to the digits of the fingers and toes.

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Ichthyosauria Triassic to Cretaceous – However, more extreme members of group lived in Jurassic and Cretaceous. Most highly specialized of marine reptiles. They converged on fish and cetacean forms. Highly modified skull: large orbit, reduced cheek region, elongate snout. Limbs modified into flippers; hyperdactyly. Viviperous: gave birth to live young.

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Most highly specialized of marine reptiles. They converged on fish and cetacean forms. Mixosaurus reconstruction

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Mosasaurs: Not closely related to Sauropterygians or Ichthyosaurs. Actually highly derived members of the lizard family Varanidae. Late Cretaceous ecological replacements for Ichthyosauria.

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Mosasaur Anatomy: Extremely elongate tail, body narrower and slimmer than other groups surveyed. (Probably swam in a more eel-like fashion.) However, neck, remains relatively short. Limbs modified for steering as opposed to propulsion. Have HYPER PHALANGY, but not hyerdactyly.